1. Field of the Invention
The present invention relates in general to automotive equipment and more particularly to an apparatus for monitoring the operation of an internal combustion engine and providing a visual display indicative of the engine operation.
2. Description of the Prior Art
Misfiring in many of todays internal combustion engines is difficult to detect, particularly for an average operator, and when detected, it can be difficult to locate the particular malfunctioning cylinder. In addition to the well known loss of engine performance and a deterioration of the fuel consumption rate in an engine which is misfiring, heat related damage can result.
In most modern internal combustion engines, a catalytic converter is used in the exhaust system for re-oxidation of combustible residues, and catalytic converters normally operate at high temperatures. When an internal combustion engine is operating in a misfiring condition, the temperature in the exhaust system increases a considerable amount above normal and such an increase of the already normally high temperature within the catalytic converter can result in burning of the catalyst.
Therefore, some method for detecting an engine misfiring condition must be employed so that corrective action can be taken before heat related damage can occur and to restore the engine to its normal fuel consumption rate and normal performance, and various methods have been proposed for this purpose.
One of these proposed methods is to monitor the electric waveform in the primary circuit, or secondary circuit, of the ignition coil of an engine. This method is not completely satisfactory, however, in that it only monitors the ignition system of the engine and misfires in a spark-ignition internal combustion engine can be caused by other factors of the engine such as an improper fuel-air mixture, a blocked fuel injector, and the like.
Another prior art method of detecting an engine misfire is to measure the temperature of the exhaust gasses being discharged from each individual cylinder of the engine and comparing these multiple temperature values with each other to detect an unusual temperature level resulting from a misfiring condition. The primary drawback with this method is that extremely complicated and costly mechanical and electrical components are required to achieve satisfactory results.
Still another method for detecting internal combustion engine misfiring is to monitor the amount of air in the exhaust gases for detecting a lack of combustion in any of the cylinders. The amount of air in exhaust gases will, of course, increase when an engine misfires as a result of the absence of combustion with a particular cylinder, or cylinders, and the increase in air concentration is sensed by an oxygen sensor located in the exhaust system. An oxygen sensor is a device which produces an electric signal that is indicative of the air concentration in the exhaust gases which pass through the sensor. The output signal from an oxygen sensor is substantially constant except when the concentration of oxygen contained in the exhaust gas assumes a certain value such as that which corresponds to the stoichiometric air-to-fuel ratio of the fuel air mixture in the fuel supply system of the engine. Thus, an oxygen sensor is unable to continuously and faithfully follow the air concentrations in exhaust gases in an analog fashion and therefore, cannot distinguish between a misfiring condition and a condition wherein an overly lean fuel mixture is combusted in an engine.
A particular prior art engine misfire detection system is disclosed in U.S. Pat. No. 4,083,234 wherein an electroacoustic transducer is provided to sense exhaust noises of an internal combustion engine and produce a continuous electric signal wave. The signal produced by the transducer has peak values appearing at a fundamental frequency irrespective of the engines firing condition and other values which occur at fractional harmonic frequencies when the engine misfires. The output signal wave of the transducer is amplified and coupled to a frequency analyzer. Another signal is provided by a frequency generator which senses engine speed and its signal is indicative of engine speed and that signal is also coupled to the frequency analyzer. The frequency analyzer modifies the signal wave received from the transducer in accordance with the engine speed signal received from the frequency generator and analyzes the fundamental frequency component of the wave and the fractional harmonics thereof to establish a relationship between the spectrum amplitudes of those signal wave components. The fractional harmonics of the signal wave are added together to produce a composite signal and a misfire signal is produced by the frequency analyzer when the spectrum density level of the composite signal becomes greater than the spectrum density level of the fundamental frequency component of the signal wave produced by the transducer. The misfire signal produced by the frequency analyzer is connected to a suitable control circuit which is operative to remedy the malfunctioning of the fuel supply system and/or the ignition system whichever caused the misfire.
As will be appreciated from the brief description presented immediately above with regard to the particular prior art misfire detection system, the system is completely automatic and as a result the vehicle's operator is left completely out of the detection and correction functions of the system. In order to accomplish the objectives of such a fully automated systems, the system itself is very complex and costly. Further, as is well known, not all engine malfunctions can be remedied by simple adjustments and therefore a control circuit cannot possibly correct everything within an engine that can cause a misfire. In addition, this particular prior art system makes no provisions for locating the particular cylinder which is misfiring, all it produces is a signal indicative of the presence of a misfire. Therefore, even if the vehicle's operator becomes aware of the misfire condition, the detection and correction system will not help the operator in locating the source of the problem.
Therefore, a need exists for a new and improved engine misfire detection system which overcomes some of the problems and shortcomings of the prior art.